I've a project with several psd layers in After effects. I made some adjustements to one of the layers with the copy stamp tool (in the extra layer window) and removed some background objects. Pre Rendering works fine, but when i render the comp, this adjusted layer just renders black. Any idea what could be wrong? The adjusted layer has this blue kind of rectangle symbol next to the layer name.

Another strange thing: when i copy this layer, all the adjustements made with the copy stamp tool are gone.

[Dennis Squadrazzino]"The adjusted layer has this blue kind of rectangle symbol next to the layer name."

That's a guide layer -- a layer that's visible in the viewer, but is NOT included when precomped or rendered for output. Select the layer, then from the Layer menu in the menu bar, click "Guide layer" to toggle.